The importance of the thymus gland in the development and senescence of immunological competence in animals and man is now generally accepted. Although there is little knowledge of the molecular events by which the thymus gland exerts control over T cell development, it appears that a vital part of the process occurs via a hormonal mechanism. The thymus produces a family of polypeptides termed thymosin and perhaps several other thymic hormones and/or factors which play an important role in the maturation, differentiation and function of T cells. Thymosin has been found to induce T cell differentiation and enhance immunological functions in genetically athymic mice, in adult thymectomized mice, in NZB mice with severe autoimmune reactions, in tumor bearing mice and in mice with casein-induced amyloidosis.
Thymosin fraction 5 is a potent immunopotentiating preparation and can act in lieu of the thymus gland to reconstitute immune functions in thymic deprived and/or immunodeprived individuals. Ongoing clinical trials with fraction 5 suggest that thymosin is effective in increasing T cell numbers and mormalizing immune function in children with thymic dependent primry immunodeficiency diseases and can increase T cell numbers in immnodepressed cancer patients.
Analytical polyacrylamide gel electrophoresis and isoelectric focusing have demonstrated that fraction 5 consists of 10-15 major components and 20 or more minor components with molecular weights ranging from 1,000 to 15,000.